1. Field of the Invention
Embodiments of the present invention relate to a tool head, in particular to a drilling head for machining a metallic workpiece, wherein the tool head has a center axis and at least two major cutting edges, which, viewed in a side view, take a convex course and define with their radially outermost region a nominal radius. Embodiments of the present invention further relate to a method for machining a metallic workpiece with a tool bearing such a tool head.
2. Background Information
In machine cutting, in particular in the drilling of hard materials, there is generally the problem of high load upon the cutting edges of the tool head. This usually has the result that only comparatively low machining rates can be set and/or a high level of wear occurs. The generated forces also occasionally lead under adverse conditions to chipping of the cutting edges.
Such problems arise in particular, for instance, in the aviation sector, in which very hard metallic materials, for instance titanium, are used. This situation is aggravated by the fact that drill holes are often made with the aid of manually operated drilling tools.
In the case of the material titanium, there is the particular problem that the chips tend to adhere or stick to the cutting edge. Succeeding cuttings can then lead to a locally very high load upon the cutting edge, so that the risk of chipping is high. Accordingly, only low feed rates can be achieved.
The cutting edge geometry of a drill can have a substantial influence on the cutting load upon the cutting edges. In a drilling head there are usually provided at least two major cutting edges, which are typically connected to one another by a chisel edge. The cutting edges run roughly radially outward and merge at a cutting corner typically into a minor cutting edge, which is continued along a chip groove in the axial direction.
Moreover, high loads also arise in respect of cast materials, for instance gray cast iron, in particular due to an inhomogeneous material structure.
EP 1 622 735 B1 discloses a drilling tool, developed specifically for the machining of cast materials, in which the major cutting edges run in a convexly curved course and subsequently, at their radially outermost point, merge into a drill back, with the formation of a bend region at a cutting corner.
Further drilling tools having convexly curved cutting edges can be derived, for instance, from U.S. Pat. No. 1,309,706 and U.S. Pat. No. 3,443,459.